Thermo-reversible Diels-Alder polymerization of difurfurylidene diglycerol and bismaleimide

Difurfurylidene diglycerol (DFDG) was synthesized by the acetalization reaction of furfural and diglycerol, both of which can be derived from renewable resources. The 1H and 13C NMR analyses revealed that DFDG is a mixture of stereoisomers. Diels-Alder (DA) polymerization of equimolar amounts of DFDG and 4,4′-bismaleimidodiphenylmethane (BMI) at 60 °C for 48 h in chloroform afforded a bio-based linear polyimide (DFDG-BMI) with Mw of 5400. Prolonged reaction time resulted in a lowering of molecular weight and an increase of exo/endo DA adduct ratio. The Mw of the polyimide obtained by the reprecipitation of DFDG-BMI (pDFDG-BMI) was 7900. The X-ray diffraction and polarized optical microscopic analyses revealed that pDFDG-BMI is a crystalline polyimide. The differential thermal analysis revealed that pDFDG-BMI had a melting temperature at 126 °C, and broad endothermic peaks at around 140-170 °C due to retro DA reaction. The retro DA depolymerization of pDFDG-BMI in N,N-dimethylformamide smoothly proceeded at around 100-120 °C to regenerate the corresponding monomers, as is obvious from the gel permeation chromatographic and 1H NMR spectral analyses.